The information used in the letters comes from a public registry that costs $20 (£15) to access. This data is typically used by political parties for voter outreach.

"What if your friends, your neighbours, and your community knew whether you vote?" the letter asks.

At the bottom of the letter, a table shows the names, addresses and voting history from the November 2014, March 2016 and November 2016 elections for the addressee's friends and neighbours.

The note also stated that after the 15 May election, the group will mail an updated chart so that "you and your friends, your neighbours, and other people you know will all know who voted and who did not vote".

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Media captionTrump voters say US president is 'doing a fabulous job'

The voter-shaming letters have prompted dozens of calls to the elections office over the past few days, the news site reported.

Election officials say the group is not a registered political action committee and it is unclear who is behind the campaign.